1. Field of the Invention
The present invention relates to a magnet used in a brushless motor used in electronic devices, a brush motor rotor or stator; a magnet with yoke; and a motor in which they are used.
2. Description of the Related Art
(Patent Reference 1) Japanese Unexamined Patent Application (Kokai) 6-124822
The need for smaller, high performance motors has been increasing in recent years. Small and high-performance brushless motors with high torque as well as low cogging torque are also needed.
Ring magnets used in brushless motors are ordinarily used having been magnetized with a plurality of poles. With respect to alignment and method of magnetization of those magnets, there are radially magnetized ring magnets and polar anisotropically magnetized ring magnets.
In comparison to polar anisotropically magnetized ring magnets, the alignment and magnetization of radially magnetized ring magnets is good, but surface magnetic flux is quite inferior, and because the magnetic flux changes abruptly at the interface between the magnetic poles there is a large amount of cogging torque, which needed to be improved.
On the other hand, in comparison to radially magnetized magnets, surface magnetic flux for polar anisotropically magnetized ring magnets is high, and because the change in magnetic flux at the interface between the magnetic poles is sinusoidal and smooth, magnetic properties are excellent. However, magnet thickness h which is about ½ the width W of one magnetic pole of the surface of a polar anisotropically magnetized ring magnet is made necessary. Therefore, magnet thickness was increased which also made the motor larger.
With respect to radially aligned ring magnets, in order to solve the above mentioned problems with radial anisotropic ring magnets and polar anisotropic ring magnets, as stated in Japanese Unexamined Patent Publication (Kokai) 6-124822, in radial anisotropic ring magnets, isotropic ring magnets are proposed on which are alternately conferred high anisotropic alignment, magnetization and low anisotropic alignment, and magnetization, but although cogging torque decreased, the torque properties were diminished.
In the anisotropic rare earth bonded magnets (particularly NdFeB magnets) among the above-stated ring magnets, compared to other anisotropic magnets requiring alignment, a large aligning magnetic field is necessary. Therefore, even if the wall thickness of the bonded magnet is made ½ the width of one magnetic pole, because sufficient magnetic flux for realizing alignment is distributed along the surface part of the ring-shaped bonded magnet, the inside part of the magnet is not aligned, and the wall thickness is not effectively utilized. That is, there is the problem of an increase in the amount of magnet material necessary for a motor which will generate the same torque. Also, as shown in FIG. 6, when the magnet is formed with a wall thickness thinner than ½ the width of the interval of one magnetic pole, because the aligning magnetic field is formed along the surface adjacent to the magnetic pole interval, orientation of the main magnetic pole is insufficient, and in anisotropic rare earth bonded magnets, realization of magnetization and polar anisotropic alignment in order to draw out motor properties is not seen, and an anisotropic rare earth bonded magnet with polar anisotropic alignment and magnetization is not known.
Thus, in rare earth bonded magnets, only radially aligned magnets could be obtained.